The present invention relates in general to shelters to protect people from building collapse or other structural failures and from flying missiles and other damage resulting from natural disasters such as hurricanes, tornadoes, earth quakes, and thunderstorms, and from other disasters such as explosions and vehicle collisions. In particular, the present invention relates to stand-alone, above-ground storm shelters which are constructed from metal plating and that can be assembled in existing houses, can be installed in houses being built, and can also be constructed as stand-alone structures.
The Federal Emergency Management Agency (FEMA) has established criteria for in-residence shelters to protect the inhabitants of buildings from natural disasters. These shelters are xe2x80x9cto provide a high degree of occupant protection during severe windstorms (hurricanes and tornadoes).xe2x80x9d In-Residence Shelter, October, 1998. This FEMA publication provides construction plans and drawings for several different types of shelters including an in-ground shelter, a basement lean-to, a corner location basement shelter, a Concrete Masonry Unit (CMU), a CMU/concrete shelter, and a wood-frame shelter with plywood sheathing or steel wall sheathing.
There is also a recently published pamphlet sponsored by FEMA and written by the Wind Engineering Research Center of Texas Tech University entitled, xe2x80x9cTaking Shelter From the Storm: Building a Safe Room Inside Your Housexe2x80x9d (First Ed., October 1998), listed as publication FEMA 320 entitled. This publication states that the basis of the design of a shelter xe2x80x9cis to provide a space where you and your family can survive a tornado or hurricane with little or no injury . . . To protect the occupants during extreme windstorms, the shelter must be adequately anchored to the house foundation to resist overturning and uplift. The connections between all parts of the shelter must be strong enough to resist failure, and the walls, roof, and door must resist penetration by windborne missiles.xe2x80x9d However, the pamphlet goes on to state that extensive testing has shown that xe2x80x9cwalls, ceilings, and doors commonly used in house construction cannot withstand the impact of missiles carried by extreme winds.xe2x80x9d The publication then describes shelter designs that meet the design criteria.
All of the shelters in the FEMA publication involve permanent construction using concrete as the primary material or as the foundation material. The installation of these shelters thus cannot be done by the average homeowner and requires the use of a professional builder. For example, the wall construction recommended for a typical frame shelter plan with plywood and steel wall sheathing includes two layers of three-quarter inch plywood panels on the outside, a 14 gage steel sheathing on the inside and double 2xc3x974 studs at 16 inches on center.
FEMA shelters have the following design criteria: they will withstand wind pressures developed from 250-MPH, 3-second gust in accordance with ASCE 7-95; they will withstand windborne debris (missile) impact loads created by a 15 pound 2xc3x974 traveling horizontally along the board""s longitudinal axis at 100 mph, traveling vertically at 67 mph, and impacting perpendicular to the wall surface. This missile speed corresponds to a 250 mph wind. The tornado missile test criteria was established by the Wind Engineering Research Center (WERC) at the Texas Tech University.
Other design criteria which has been set by FEMA for in-ground shelters includes that it has inside space for an in-ground shelter of a minimum of five square feet per person.
The shelter design criteria have contradictory requirements: on the one hand the shelters must be physically strong so that they can withstand high wind and earthquake forces; and on the other hand, the shelters must also be able to withstand the penetration of wind borne articles. If the shelter is constructed pursuant to the plans in the aforementioned FEMA publication, it can easily meet both of these contradictory criteria. However, such a shelter must be constructed by a professional building contractor that has a number of different professional workers, each with one of the requisite construction skills such as masonry, carpentry, and iron work.
There are many U.S. patents which disclose many varieties of shelters. Invariably, all of these shelters have the primary goal of providing structural integrity and protecting against collapse, ignoring the protection against the penetration of wind borne articles. One recently issued Wailer, U.S. Pat. No. 5,813,174, incorporated herein by reference, discloses a light-weight steel structure that can be packaged and shipped as loose tubular and bent-plate channel modules and can be assembled by the user. The patent disclosure states that this structure can be assembled entirely from inside the structure as it is being built and thus can be installed in an existing enclosure. It appears that an embodiment of this patent is presently being marketed by the Remagen Corporation of Monteagle, Tenn. However, the whole intent of this patent is to produce a structure comprised of a plurality of metal panels bolted together so as to produce extremely rigid walls that provide a solid enclosure. The construction features set forth in this patent clearly describe an I-beam configuration between adjacent panels that are connected to a rigid frame. For example, FIG. 5 of the patent discloses a rigid frame that is comprised of square, hollow steel tubes that defines the parallelepiped shape of the structure. Each end of each wall panel has a rigid metal cap at each end that is rigidly connected to the frame to provide increased rigidity.
The difficulty with such a very rigid and solid structure is that it will not pass the FEMA penetration test simply because it is too rigid. They are designed to protect against building collapse. There is virtually no xe2x80x9cgive xe2x80x9d or xe2x80x9cplay xe2x80x9d in the walls, and thus no means for absorbing and distributing the striking force of a propelled object, such as a 2xc3x974 beam traveling at over 100 miles per hour. As stated in the publication FEMA 320, at page 12:
Damage can also be caused by flying debris (referred to as windborne missiles). If wind speeds are high enough, missiles can be thrown at a building with enough force to penetrate windows, walls, or the roof . . . Even a reinforced masonry wall will be penetrated unless it has been designed and constructed to resist debris impact during extreme winds. Because missiles can severely damage and even penetrate walls and roofs, they threaten not only buildings but the occupants as well.
Thus, there is a need for a shelter that will not only meet the aforesaid contradictory FEMA criteria, but also can be assembled by the consumer without the need for professional builders. There is also a need for a shelter that can be constructed in a reasonable period of time in an existing inhabited building without causing too much disruption. In addition, there is a need for such a shelter that can be economically purchased and easily assembled with only common hand tools. Thus it is clear that there is a long felt, well recognized need for a personnel shelter that can be economically assembled by relatively unskilled workers, in fact by a single consumer, from prefabricated components with readily available hand tools in a short period of time, and still when assembled can pass both the structural integrity tests and the missile penetration tests.
One of the key features of the present invention is the finding that a lightweight prefabricated structure (prefab) can meet both the structural strength and penetration tests only if its walls are designed to absorb and dissipate the energy from high speed missile impacts. Such an invention satisfies all of the aforesaid needs. It not only passed the penetration test of one missile, it passed the penetration test of three, subsequently fired missiles. It is economical to manufacture and purchase. It can be easily shipped in a plurality of modules and assembled by the consumer using readily available tools.
The present invention provides a modular, above-ground protective shelter designed to be used by the occupants as a protective refuge to protect them against injury from structural failure and/or flying missiles resulting form disasters such as tornadoes, severe thunderstorms, hurricanes, earth quakes, explosions, etc. It has the advantages that it can be obtained in a partially prefabricated form or in disassembled packages that can be readily assembled and easily retrofitted into existing buildings or installed in new construction buildings. The present invention utilizes diaphragm construction and has individual components that are sized so that they can be handled and installed by one person who need not be highly skilled or a professional. The present shelter is made from materials that have the strength to meet the design load criteria such as FRP, steel, high strength steel, aluminum, kevlar, carbon fiber, etc, or a combination of two or more of them.
According to one embodiment of the present invention, the shelter is comprised of a base, four walls supported on the base, and a roof supported by the four walls such that the four walls and roof define an interior space. Each wall is comprised of a plurality of elongate panels that have a top end, a bottom end and parallel sides, each panel being connected only at the sides thereof to a corresponding side of an adjacent panel, at the top to said roof, and at the bottom to the base so as to form a diaphragm. Each panel has a channel shape with a xe2x80x9ccxe2x80x9d shaped cross section and is comprised of an elongate web portion having side edges and two integral flange portions that extend into said interior space and terminate at inward edges. A plurality of longitudinally spaced, mechanical fasteners extend through adjacent flange portions of adjacent panels near the inward edges thereof so that the outward portions can flex apart.
While the present invention utilizes similar materials that are used in the aforementioned Waller patent, the materials are connected together in an entirely different way in the present invention so as to provide a diaphragm type design that distributes the collapsing forces of the wind to the adjacent walls, on the one hand, and absorbs the kinetic energy of the missile through the controlled deformation of both the struck panel and the adjacent panels, on the other hand, resulting in a structure that both prevents the penetration of wind borne missiles and withstands the collapsing forces of wind storms. Thus, the particular construction design of a structure that can both repel missiles and withstand collapsing forces is very important, but according to experts in the field, is not deducible from the prior art. As stated in a writing entitled, xe2x80x9cConsiderations in Designing Above-Ground Storm Shelters,xe2x80x9d from the Wind Engineering Research Center (WERC) of Texas Tech University, which is the author of FEMA 320 publication:
Structural analysis and design are sufficiently mature to permit analytical approaches to be used to assure structural integrity of shelters when subjected to wind-induced forces. On the other hand, the resistance to perforation of common residential building components by wind-borne debris does not lend itself to analytical solution. Performance testing seems necessary to assure reliability.
Building a strong rigid structure with relatively light material is easy. However, because the elastic curve of steel under high velocity impact is markedly different than from static loading and the capacity of steel to absorb energy without rupture is considerably less than under impact at moderate speeds, resisting penetration from high velocity impact with relatively light material is difficult. The structure must be designed and constructed so that there is enough give at impact to initiate deformation. The combination of xe2x80x9cgivexe2x80x9d and controlled deformation allow the structure to prevent penetration.
The present invention satisfies a number of design criteria to obtain its above listed objects and features, which criteria is not obvious from the prior art. Together these criteria include: a shelter that is comprised of components that can be handled by a single person and can be installed by a single person using only hand tools and the contradictory criteria that such a shelter will provide protection from the tremendous forces and prevent penetration by flying missiles; a shelter that has a retail cost that is far below the costs of contemporary designs; a shelter that can accommodate a family; a shelter that can be prefabricated; a shelter that can be manufactured in one part of the country and easily and economically shipped to the locations where it is needed; and a shelter which if damaged can be easily and economically repaired. The present invention meets all of these design criteria.
However, there are other features, advantages and benefits of the present invention, and they together with those listed above will be set forth in or obvious from the detailed description of the invention hereinbelow.